Returns (as multiple values) a list of points for an ROC curve and a list of
f-measures associated with those points. The ROC curve algorithm is from Tom
Facwett’s ROC Graphs: Notes and Practical Considerations for Data Mining Researchers.
See moab entry fawcett-roc-2003 for more information.

If you know that the examples are already sorted, you can use the sort? keyword to
prevent this from sorting them again. The :beta keyword is passed along to the
f-measure function. The :weight keyword is provided to handles aggreates of examples.